A method for measuring complex impedance of a motor bearing in situ

Abstract

The application provides a kind of method for in-situ measurement motor bearing complex impedance, it is related to motor fault diagnosis technical field.The application constructs measurement bridge structure based on AC unbalance Wheatstone bridge principle, deduces bearing equivalent impedance model using the phase and amplitude relationship between bridge voltage signal and excitation signal.Through the differential collection of bearing inner ring and outer ring potential, combined with high-frequency AC excitation, standard impedance matching and differential signal measurement, under the premise of not changing the motor structure, realize high-precision measurement of bearing impedance, have strong anti-interference ability, can adapt to various working conditions of motor structure layout, especially suitable for embedded, in-situ, real-time impedance detection application scene.The method of the application can realize in-situ, high-precision measurement of bearing internal state, lay a solid foundation for future expansion to motor condition diagnosis and intelligent maintenance system, has good engineering practical value and popularization prospect.

Description

Technical Field

[0001] This invention relates to the field of motor fault diagnosis technology, and in particular to a method for in-situ measurement of complex impedance of motor bearings. Background Technology

[0002] As industrial equipment develops towards higher automation and reliability, higher demands are placed on the online monitoring of motor operating status. As a critical support component in a motor, the operating status of bearings directly affects the overall performance and lifespan of the machine. Therefore, how to achieve accurate detection of bearing status has become an important research direction in the field of motor operation and maintenance.

[0003] Current methods for detecting the condition of motor bearings mainly rely on vibration analysis, temperature monitoring, and current signal analysis. However, these methods all suffer from problems such as response lag, high environmental sensitivity, or limited applicability, making it difficult to meet the early detection needs of minute structural changes. In contrast, impedance measurement, due to its high sensitivity to changes in lubrication and contact conditions, has become a hot research topic in recent years.

[0004] Although impedance-based measurement methods have been proposed, they still face several challenges in practical engineering applications: First, the complex structure of motors leads to significant interference noise and unstable contact during measurement, resulting in poor impedance signal quality. Second, traditional impedance measurement methods rely on expensive instruments, making them difficult to integrate into motor systems for in-situ monitoring. Third, ensuring stable injection and accurate sampling of high-frequency excitation signals during rotation is a key technical challenge that urgently needs to be addressed in the engineering of impedance measurement. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to address the shortcomings of the prior art by providing a method for in-situ measurement of the complex impedance of motor bearings. By differentially acquiring the potential of the inner and outer rings of the bearing, and combining high-frequency AC excitation, standard impedance matching and differential signal measurement, high-precision measurement of bearing impedance can be achieved without changing the motor structure. It has strong anti-interference ability, can adapt to motor structure layout under various working conditions, and is particularly suitable for embedded, in-situ, and real-time impedance detection applications.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0007] A method for in-situ measurement of the complex impedance of motor bearings, based on the principle of an AC unbalanced Wheatstone bridge, constructs a measurement bridge structure and derives the equivalent impedance model of the bearing using the phase and amplitude relationship between the bridge voltage signal and the excitation signal; including the following steps:

[0008] Step 1: Prepare the motor wiring;

[0009] The outer ring of the bearing can be directly or indirectly connected. In the case of indirect connection, a dielectric pad is used to isolate the bearing from the motor body, and the outer ring of the bearing contacts the motor end cover. Current is coupled to the end cover, and the voltage of the outer ring of the bearing is obtained by measuring the voltage at the end cover. In scenarios where the voltage of the outer ring of the bearing needs to be directly obtained, an effective electrical connection with the outer ring of the bearing is achieved in two ways to acquire the voltage signal: First, an annular dielectric pad is installed on the outer ring of the bearing as a transition / insulation adapter for the electrical connection; second, insulating varnish is applied to the surface of the outer ring of the bearing to ensure insulation of non-acquisition areas, and a dedicated probe is used to directly contact the target acquisition area on the outer ring of the bearing. The inner ring of the bearing is fixedly connected to the motor spindle. The current generated during motor operation is transmitted to the spindle through coupling, and then conducted to the inner ring of the bearing fixed to the spindle. The voltage of the inner ring of the bearing is obtained through a slip ring or carbon brush connected to the spindle.

[0010] Step 2: Set up an AC unbalanced Wheatstone bridge measurement system. The system includes a frequency converter AC power supply, an AC unbalanced Wheatstone bridge, a digital differential oscilloscope, a data processing and transmission device, and computer software.

[0011] The variable frequency AC power supply is used to provide a stable high-frequency carrier signal for the measurement system. Its output frequency and amplitude are adjustable, and it is used to excite the bearing branch under test. The AC unbalanced Wheatstone bridge consists of known reference impedances Z1, Z2, and Z3 and the unknown bearing impedance Z. x The input impedance Z of a digital differential oscilloscope m As part of the measurement branch, one arm of the bridge circuit is replaced by the bearing under test, forming an unbalanced bridge structure. The bridge voltage v is measured. m With frequency converter voltage v gen The bearing impedance is then calculated; a digital differential oscilloscope is used to synchronously acquire the bridge voltage V. m With frequency converter voltage v gen The system outputs the original waveform signal at a sampling rate no less than twice the carrier frequency. The data processing and transmission device is responsible for preprocessing, impedance calculation, and data transmission of the acquired voltage signal. The preprocessing process includes signal synchronization, filtering, missing value repair, and amplitude normalization. The complex impedance Z is automatically calculated based on a phase-amplitude demodulation algorithm. x The real part, imaginary part, magnitude and phase angle of the sampled signal; the computer host computer software serves as the core control and display platform of the system. Its functional modules include communication and control, data visualization and analysis, and data storage and export. It can realize the real-time reception and calculation control of the sampled signal, visualize the calculated complex impedance, resistance, capacitance and phase angle parameters as curves or Nyquist plots, and realize the automatic storage and formatted output of measurement data.

[0012] Step 3: Connect the AC unbalanced Wheatstone bridge circuit. Connect the motor's current-carrying carbon brush as the positive terminal of the bearing to the circuit, and connect the bearing outer ring or motor housing as the negative terminal of the bearing to the circuit. Note that grounding is required.

[0013] Step 4: Turn on the inverter AC power supply and adjust the amplitude and frequency of the target sinusoidal voltage output by the power supply;

[0014] Step 5: Use an oscilloscope or high-speed acquisition card to compare the bridge voltage V using an AC unbalanced Wheatstone bridge. m and frequency converter power supply voltage V gen For measurement and data acquisition, the sampling rate must be greater than twice the power carrier frequency;

[0015] Step 6: The data processing and transmission device preprocesses the acquired data, including signal synchronization, filtering, missing value repair, and amplitude normalization; then, it automatically calculates the complex impedance Z based on the phase-amplitude demodulation algorithm. x The real part, imaginary part, magnitude, phase angle, and parallel capacitance of the bearing impedance equivalent circuit. and parallel resistors ;

[0016] Step 7: Send the calculated complex impedance to a remote computer for visualization using computer software.

[0017] Furthermore, the specific method for step 6 is as follows:

[0018] Assuming the power supply voltage phase arg(v) gen =0°, and according to Kirchhoff's laws, the complex impedance equation containing the probe impedance is derived as follows:

[0019] (1);

[0020] in, The complex signal of the bridge voltage, v gen This is the real signal of the frequency converter power supply voltage. For the complex form of the reference impedance Z1, For bearing complex impedance;

[0021] Centered on sample index k, N samples are symmetrically covered, and then discrete cross-correlation is performed on these N samples; to obtain To determine the correct amplitude of the voltage ratio by using the real part of the voltage, the correlation with the supply voltage needs to be multiplied by [the factor]. ,in Power supply voltage The amplitude estimate; for calculation The imaginary part requires the input voltage to be obtained first. 90° phase shift signal , yes The orthogonal signals are used to construct the imaginary component of the voltage ratio, and then the result is obtained by combining the probe with the relevant components through calculation; the corresponding formula is as follows:

[0022] (2);

[0023] (3);

[0024] in, Represents the real part of a complex number. Represents the imaginary part of a complex number; This indicates the measured voltage at sample index k. With power supply voltage The voltage ratio is in complex form; K is the sample index sequence, identifying the current time point / sample position in the calculation; N is the number of samples to move the summation window. Power supply voltage The amplitude estimate is used for normalization; The measured voltage at the i-th sample point The value of , where _ represents the complex form of the data; The power supply voltage at the i-th sample point The value; This indicates that a discrete cross-correlation summation operation is performed on the samples within a window centered at k and of length N; At the i-th sample point The 90° phase-shifted signal is used to calculate the imaginary part of the voltage ratio;

[0025] Subsequently, the application cutoff frequency is f m A first-order low-pass filter of / 2 eliminates any residual ripple and avoids misinterpretation of the signal; to reduce the influence of stray capacitance and cable inductance, open-circuit-short-circuit calibration is required. Therefore, the impedance Z is measured when the device under test is removed. open Measure the impedance Z during short circuit short , used to obtain the measured impedance Z through equation (4) x The impedance of the device under test is inferred from the middle.

[0026] (4);

[0027] in, To perform bearing complex impedance after open-circuit and short-circuit calibration; The short-circuit impedance measured when the bearing is short-circuited; This refers to the short-circuit complex impedance measured when the bearing is open-circuited;

[0028] Finally, at the carrier frequency Down, Given the power supply carrier frequency, the parallel capacitance C in the equivalent circuit of the bearing impedance of a single-bearing motor is... DUT and parallel resistor R DUT The calculation is as follows:

[0029] (5);

[0030] (6);

[0031] For a dual-bearing rotary motor, an improved three-arm AC unbalanced Wheatstone bridge is used to measure the impedance of the two bearings. Specifically, based on the original AC unbalanced Wheatstone bridge, a branch with the same structure as the left arm is added next to the right arm, and a reference impedance is set at the top of the arm. The lower part is connected to the second bearing to measure the impedance. The voltage difference between the output terminals of the two bridge arms on the right is denoted as . This is used to reflect the bridge voltage signal of the second bearing branch; by measuring separately and And in combination with the corresponding frequency converter voltage Using the reference impedance parameters, the complex impedances of the two bearings without open-circuit or short-circuit calibration are obtained, and the calculation formulas are as follows:

[0032] (7);

[0033] (8);

[0034] in, , , , The complex impedance of the bearing connected to the left side of the bridge when it has not been calibrated with an open-circuit and short-circuit circuit is given. The complex impedance of the bearing connected to the right side of the bridge when it has not been calibrated with an open circuit and short circuit.

[0035] Finally, the calculated uncalibrated complex impedance is... and As measured impedance respectively Substituting into formula (4) for open-circuit-short-circuit calibration, the calibrated bearing complex impedance is obtained. and ; and then and As respectively Substituting into formulas (5) and (6), the equivalent capacitances of the two bearings are calculated. and equivalent resistance .

[0036] Furthermore, the digital differential oscilloscope acquires data at a predetermined sampling rate and sampling interval, and uses a differential voltage probe CH1 to measure the inverter power supply voltage V. gen The differential voltage probe CH2 was used to measure the bridge voltage v. m .

[0037] The beneficial effects of adopting the above technical solution are as follows: The method for in-situ measurement of the complex impedance of motor bearings provided by this invention can realize online measurement of motor bearing impedance, adapting to the dynamic testing requirements under rotating conditions; by introducing an AC unbalanced Wheatstone bridge structure, the influence of stray impedance can be reduced, improving measurement stability and anti-interference capability; a standardized measurement process is proposed, including wiring method, parameter configuration, filtering, open and short circuit calibration, etc., ensuring the consistency and repeatability of measurement results; combined with the bridge measurement model, a calculation method from bridge voltage signal to bearing complex impedance is established to obtain complete equivalent parameters including resistance, capacitance, phase angle, etc. The method of this invention can realize in-situ, high-precision measurement of the internal state of bearings, laying a solid foundation for future expansion into motor condition diagnosis and intelligent maintenance systems, and has good engineering practical value and promotion prospects. Attached Figure Description

[0038] Figure 1 A schematic diagram of the circuit connection for measuring bearing impedance using an AC unbalanced Wheatstone bridge provided in an embodiment of the present invention;

[0039] Figure 2 A structural diagram of an AC unbalanced Wheatstone bridge provided in an embodiment of the present invention;

[0040] Figure 3 A diagram of the improved AC unbalanced Wheatstone bridge structure provided in an embodiment of the present invention;

[0041] Figure 4 This is a schematic diagram illustrating the indirect connection of the bearing outer ring according to an embodiment of the present invention;

[0042] Figure 5 This is a schematic diagram illustrating the direct connection of the bearing outer ring according to an embodiment of the present invention;

[0043] Figure 6 A schematic diagram of the overall modification of an AC unbalanced Wheatstone bridge for measuring bearing impedance in a physical motor, provided in an embodiment of the present invention; wherein, (a) is the front view and (b) is the left view;

[0044] Figure 7 A schematic diagram of the modification of the motor end cover for measuring the bearing impedance of a physical motor using an AC unbalanced Wheatstone bridge provided in an embodiment of the present invention; wherein, (a) is the front view and (b) is the left view;

[0045] Figure 8 The graph shows the modulus results from the measurement data provided in this embodiment of the invention under operating conditions of 1000 N / min, 30° oil temperature, and 1000 N radial load.

[0046] Figure 9 The equivalent resistance result diagram is provided in the measurement data of the embodiment of the present invention under the operating conditions of 1000 N / min, 30° oil temperature, and 1000 N radial load.

[0047] Figure 10 The equivalent capacitance result diagram is provided in the measurement data of the embodiment of the present invention under the operating conditions of 1000 N / min, 30° oil temperature, and 1000 N radial load.

[0048] Figure 11 The phase angle result diagram is provided in the measurement data of the embodiment of the present invention under the operating conditions of 1000 N / min, 30° oil temperature, and 1000 N radial load.

[0049] Figure 12 The diagram shows the real part of the bearing complex impedance from the measurement data provided in this embodiment of the invention under operating conditions of 1000 N / min, 30° oil temperature, and 1000 N radial load.

[0050] Figure 13 The diagram shows the imaginary part of the bearing complex impedance from the measurement data provided in this embodiment of the invention under the operating conditions of 1000 N / min, 30° oil temperature, and 1000 N radial load. Detailed Implementation

[0051] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0052] like Figure 1 As shown, the method in this embodiment uses an AC unbalanced Wheatstone bridge to measure the bearing impedance, as detailed below.

[0053] First, prepare the motor wiring.

[0054] A dielectric pad is used to isolate the bearing from the motor body. The outer ring of the bearing contacts the motor end cover, and current is coupled to the end cover. The voltage of the outer ring of the bearing is obtained by measuring the voltage at the end cover. Alternatively, the outer ring of the bearing can be secured by installing a ring-shaped dielectric pad or by applying insulating varnish to the outer ring and contacting it with a probe. The inner ring of the bearing can be fixed to the motor spindle and current-coupled to the spindle. The voltage of the inner ring of the bearing is then obtained through a slip ring or carbon brush connected to the spindle.

[0055] Then, measurements were taken using an AC unbalanced Wheatstone bridge.

[0056] An unbalanced AC Wheatstone bridge measurement system was constructed, which includes a frequency converter, an AC unbalanced Wheatstone bridge, a digital differential oscilloscope, a data processing and transmission device, and computer software.

[0057] Specifically, the frequency converter provides a stable high-frequency carrier signal, and a digital differential oscilloscope measures the voltage values ​​at two points on the bridge. The measurement data is then remotely transmitted to a computer via data processing and transmission devices, where it is visualized by the computer's host software. The AC unbalanced Wheatstone bridge includes known reference impedances Z1, Z2, and Z3. m The impedance is the oscilloscope impedance, which can be found in the oscilloscope manual. The rolling bearing under test is taken as the unknown impedance Z. x Connect the bridge circuit; a digital differential oscilloscope is used to measure the bridge voltage V. m and power supply voltage v gen Its structure is as follows Figure 2 As shown in the figure. With the above system configuration, high-precision measurement of bearing complex impedance can be achieved without changing the motor structure. It has good anti-interference ability and real-time performance, providing reliable data support for subsequent bearing condition monitoring and electro-erosion mechanism analysis.

[0058] Assuming the power supply voltage phase arg(v) gen =0°, and based on Kirchhoff's laws, derive the complex impedance equation containing the probe impedance:

[0059] (1);

[0060] in The complex signal of the bridge voltage, v gen This is the real voltage signal from the signal generator.

[0061] Since phase information cannot be reliably derived from a single sample, a moving summation method is employed, which symmetrically covers N samples around k. Then, discrete cross-correlation is performed on these N samples. The correlation with the supply voltage is calculated by multiplying by... get The real part is calculated to obtain the correct amplitude of the voltage ratio. To calculate the imaginary part, the input voltage v needs to be calculated. gen *90° phase shift signal.

[0062] (2);

[0063] (3);

[0064] Subsequently, the application cutoff frequency is f mA first-order low-pass filter of / 2 is used to eliminate any residual ripple and avoid misinterpretation of the signal, as high-frequency signals cannot be reliably measured. Open-circuit / short-circuit calibration is required to reduce the effects of stray capacitance and cable inductance. Therefore, the impedance Z is measured when the device under test (DUT) is removed. open Measure the impedance Z during short circuit short These values ​​are used to obtain the measured impedance Z from the equation (4). x The impedance of the DUT is calculated by reverse calculation.

[0065] (4);

[0066] Finally, at the carrier frequency Below, the parallel capacitance C of the equivalent circuit DUT and resistance R DUT Computable

[0067] (5);

[0068] (6);

[0069] For a dual-bearing rotary motor, this embodiment proposes an improved three-arm AC unbalanced Wheatstone bridge for simultaneously measuring the bearing impedance at both the drive and non-drive ends, such as... Figure 3 As shown. Specifically, based on the original AC unbalanced Wheatstone bridge, a branch with the same structure as the left bridge arm is added next to the right bridge arm, and a reference impedance is set at the upper part of the bridge arm. The lower part is connected to the second bearing to measure the impedance. The voltage difference between the output terminals of the two bridge arms on the right is denoted as . This is used to reflect the bridge voltage signal of the second bearing branch. The calculation principle of this improved structure is consistent with the single bearing impedance measurement method, by measuring the bridge voltage signal of the original first bearing branch. and the bridge voltage signal of the second bearing branch added later. And combined with the corresponding excitation voltage Given the reference impedance parameters, the complex impedances of the two bearings without open-circuit or short-circuit calibration can be obtained separately. The calculation formulas are as follows:

[0070] (7);

[0071] (8);

[0072] in, , , . The complex impedance of the bearing connected to the left side of the bridge when it has not been calibrated with an open-circuit and short-circuit circuit is given. The complex impedance of the bearing connected to the right side of the bridge without open-circuit and short-circuit calibration.

[0073] Finally, the calculated uncalibrated complex impedance is... and As measured impedance respectively Substituting into formula (4) for open-circuit-short-circuit calibration, the calibrated bearing complex impedance is obtained. and ; and then and As respectively Substituting into formulas (5) and (6), the equivalent capacitances of the two bearings are calculated. and equivalent resistance .

[0074] The specific implementation steps of the proposed measurement plan are as follows:

[0075] Step 1: The outer ring of the bearing can be connected directly or indirectly. Indirect connection is as follows: Figure 4 As shown, a dielectric pad is used to isolate the bearing from the motor body, and plastic or plastic-coated fasteners are used for connection. The outer ring of the bearing contacts the motor end cover, and current is coupled to the end cover. The voltage of the bearing outer ring is obtained by measuring the voltage at the end cover. Direct connection is as follows: Figure 5 As shown, the bearing outer ring can be made by installing an annular dielectric pad on the bearing outer ring or by applying insulating varnish to the bearing outer ring and using a probe to contact the bearing outer ring; the bearing inner ring can be fixed to the motor spindle and coupled to the spindle with current, and the bearing inner ring voltage can be obtained through the slip ring or carbon brush connected to the spindle.

[0076] Step 2: Connect the AC unbalanced Wheatstone bridge circuit. Connect the motor's current-carrying carbon brush as the positive terminal of the bearing to the circuit, and connect the bearing outer ring or motor housing as the negative terminal of the bearing to the circuit. Note that it should be grounded.

[0077] Step 3: Turn on the inverter AC power supply and adjust the amplitude and frequency of the target sinusoidal voltage output by the power supply.

[0078] Step 4: Perform open-circuit-short-circuit calibration and calculate Z according to the formula. open Z short， Reduce the impact of stray capacitance and cable inductance.

[0079] Step 5: The digital differential oscilloscope acquires data at a predetermined sampling rate and sampling interval, and the differential voltage probe CH1 measures the inverter power supply voltage V. gen The differential voltage probe CH2 was used to measure the bridge voltage v. m .

[0080] Step 6: The data processing and transmission device preprocesses the acquired data, including signal synchronization, filtering (Han window processing), missing value repair, and amplitude normalization. Then, based on a pre-written program and a phase-amplitude demodulation algorithm, it automatically calculates the complex impedance, including the real part, imaginary part, phase angle, magnitude, resistance value, and capacitance value. Finally, it sends the data to a remote computer.

[0081] Step 7: After receiving the data on the computer, it is visualized and analyzed by the host computer. This data can be used for bearing lubrication status monitoring, status monitoring, etc.

[0082] Based on the above scheme, the peak value of the power supply sine wave does not exceed 3V, the frequency is between 20kHz and 100kHz, the oscilloscope sampling rate is not less than twice the carrier frequency, and Z1, Z2, and Z3 are resistors and capacitors connected in parallel. Taking a three-phase asynchronous motor of model Y2-80 FT100 as an example, the specific implementation process of the method for measuring and analyzing the motor bearing impedance using an AC unbalanced Wheatstone bridge described in this embodiment is explained.

[0083] First, disconnect the motor from the power supply and disassemble it appropriately to ensure contact with the outer and inner rings of the bearing to be tested. For example... Figure 6 , Figure 7 As shown, a dielectric pad is used to isolate the end cap from the motor body to ensure that there is no electrical short circuit during the measurement process. Conductive probes or carbon brushes are connected to the inner ring of the bearing (fixed to the shaft) and the outer ring of the bearing (connected to the motor end cap or after being treated with an insulating coating) respectively, forming the impedance branch Zx to be measured.

[0084] Secondly, build such Figure 2 The diagram shows an AC unbalanced Wheatstone bridge measurement system. The system is configured with Z1 = 1 MΩ || 1 nF, Z2 = MΩ || 1 nF, Z3 = 1.2 MΩ || 1 nF, and Z... m The internal resistance of the differential oscilloscope is set to 1MΩ∥150pF (after consulting the manual). The carrier signal is provided by a frequency converter, and the output sine wave signal has an amplitude of 2.5Vpp and a frequency set to 25kHz.

[0085] Subsequently, the motor and measuring device were started, and a differential oscilloscope was used to measure the voltage (V) of the signal generator. gen ) and bridge arm output voltage (V m Synchronous sampling was performed, with the oscilloscope set to a sampling rate of 500 kS / s to ensure signal integrity. The acquired signal was filtered and denoised using the data processing module, and the complex impedance Z was calculated using the phase-amplitude demodulation algorithm derived in this paper. x The parameters include the real part, imaginary part, and phase angle.

[0086] Next, an open-circuit-short-circuit calibration experiment was performed, and Z was measured. open With Zshort The values ​​are 3MΩ and 1.2Ω respectively. Substituting these values ​​into the compensation formula, the measured Z... x Corrections are made. The equivalent bearing resistance R is calculated based on formulas (5) and (6). DUT With parallel capacitor C DUT Parameters such as these.

[0087] Finally, the measured data was visualized and analyzed using host computer software. Figures 8-13 The measurement data are presented under operating conditions of 1000 N / min, 30°C oil temperature, and 1000 N radial load. Figure 8 The result is a graph showing the modulus values. Figure 9 The diagram shows the equivalent resistance results. Figure 10 The diagram shows the equivalent capacitance results. Figure 11 The phase angle result diagram is shown below. Figure 12 The diagram shows the real part of the bearing complex impedance. Figure 13 The diagram shows the imaginary part of the bearing complex impedance.

[0088] In summary, this embodiment verifies the feasibility and effectiveness of the proposed method for measuring and analyzing motor bearing impedance based on an AC unbalanced Wheatstone bridge. It can achieve in-situ, high-precision measurement of the internal state of the bearing, and has good engineering practical value and promotion prospects.

[0089] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope defined by the present invention.

Claims

1. A method for in-situ measurement of the complex impedance of motor bearings, characterized in that: The method is based on the principle of an unbalanced AC Wheatstone bridge to construct a measurement bridge structure, and derives the equivalent impedance model of the bearing by utilizing the phase and amplitude relationship between the bridge voltage signal and the excitation signal; it includes the following steps: Step 1: Prepare the motor wiring; The outer ring of the bearing can be directly or indirectly connected. In the case of indirect connection, a dielectric pad is used to isolate the bearing from the motor body, and the outer ring of the bearing contacts the motor end cover. Current is coupled to the end cover, and the voltage of the outer ring of the bearing is obtained by measuring the voltage at the end cover. In scenarios where the voltage of the outer ring of the bearing needs to be directly obtained, an effective electrical connection with the outer ring of the bearing is achieved in two ways to acquire the voltage signal: First, an annular dielectric pad is installed on the outer ring of the bearing as a transition / insulation adapter for the electrical connection; second, insulating varnish is applied to the surface of the outer ring of the bearing to ensure insulation of non-acquisition areas, and a probe is used to directly contact the target acquisition point on the outer ring of the bearing. The inner ring of the bearing is fixedly connected to the motor spindle. The current generated during motor operation is transmitted to the spindle through coupling, and then conducted to the inner ring of the bearing fixed to the spindle. The voltage of the inner ring of the bearing is obtained through a slip ring or carbon brush connected to the spindle. Step 2: Set up an AC unbalanced Wheatstone bridge measurement system. The system includes a frequency converter AC power supply, an AC unbalanced Wheatstone bridge, a digital differential oscilloscope, a data processing and transmission device, and computer software. The variable frequency AC power supply is used to provide a stable high-frequency carrier signal for the measurement system. Its output frequency and amplitude are adjustable, and it is used to excite the bearing branch under test. The AC unbalanced Wheatstone bridge consists of known reference impedances Z1, Z2, and Z3 and the unknown bearing impedance Z. x The input impedance Z of a digital differential oscilloscope m As part of the measurement branch, one arm of the bridge circuit is replaced by the bearing under test, forming an unbalanced bridge structure. The bridge voltage is measured. v m With frequency converter voltage v gen The bearing impedance is then calculated; a digital differential oscilloscope is used to synchronously acquire the bridge voltage. v m With frequency converter voltage v gen The system outputs the original waveform signal at a sampling rate no less than twice the carrier frequency. The data processing and transmission device is responsible for preprocessing, impedance calculation, and data transmission of the acquired voltage signal. The preprocessing process includes signal synchronization, filtering, missing value repair, and amplitude normalization. The complex impedance Z is automatically calculated based on a phase-amplitude demodulation algorithm. x The real part, imaginary part, magnitude and phase angle of the sampled signal; the computer host computer software serves as the core control and display platform of the system. Its functional modules include communication and control, data visualization and analysis, and data storage and export. It can realize the real-time reception and calculation control of the sampled signal, visualize the calculated complex impedance, resistance, capacitance and phase angle parameters as curves or Nyquist plots, and realize the automatic storage and formatted output of measurement data. Step 3: Connect the AC unbalanced Wheatstone bridge circuit. Connect the motor's current-carrying carbon brush as the positive terminal of the bearing to the circuit, and connect the bearing outer ring or motor housing as the negative terminal of the bearing to the circuit. Note that grounding is required. Step 4: Turn on the inverter AC power supply and adjust the amplitude and frequency of the target sinusoidal voltage output by the power supply; Step 5: Use an oscilloscope or high-speed acquisition card to compare the bridge voltage using an AC unbalanced Wheatstone bridge. v m and frequency converter voltage v gen For measurement and data acquisition, the sampling rate must be greater than twice the power carrier frequency; Step 6: The data processing and transmission device preprocesses the acquired data, including signal synchronization, filtering, missing value repair, and amplitude normalization; then, it automatically calculates the complex impedance Z based on the phase-amplitude demodulation algorithm. x The real part, imaginary part, magnitude, phase angle, and parallel capacitance of the bearing impedance equivalent circuit. and parallel resistors The specific method is as follows: Assuming the power supply voltage phase arg( v gen =0°, and according to Kirchhoff's laws, the complex impedance equation containing the probe impedance is derived as follows: （1）； in, The complex signal of the bridge voltage. v gen This is the real signal of the frequency converter power supply voltage. For the complex form of the reference impedance Z1, For bearing complex impedance; Symmetrical coverage centered on sample index k N One sample, then... N Perform discrete cross-correlation calculations on each sample; to obtain To determine the correct amplitude of the voltage ratio by using the real part of the voltage, the correlation with the supply voltage needs to be multiplied by [the factor]. ,in Power supply voltage The amplitude estimate; for calculation The imaginary part requires the input voltage to be obtained first. 90° phase shift signal , yes The orthogonal signals are used to construct the imaginary component of the voltage ratio, and then the result is obtained by combining the probe with the relevant components through calculation; the corresponding formula is as follows: （2）； （3）； in, Represents the real part of a complex number. Represents the imaginary part of a complex number; Indicates in the sample index k At the location, the voltage being measured With power supply voltage The voltage ratio is in complex form; K This is a sample index sequence, identifying the current calculation time point / sample location; N The number of samples to move the summation window; Power supply voltage The amplitude estimate is used for normalization; For the first i The measured voltage at each sample point The value of , where _ represents the complex form of the data; For the first i Power supply voltage at each sample point The value; Indicates to k Centered on, with a length of N The samples within the window are subjected to discrete cross-correlation summation. For the first i At each sample point The 90° phase-shifted signal is used to calculate the imaginary part of the voltage ratio; Subsequently, the application cutoff frequency is f m A first-order low-pass filter of / 2 eliminates any residual ripple and avoids misinterpretation of the signal; to reduce the influence of stray capacitance and cable inductance, open-circuit-short-circuit calibration is required; therefore, impedance is measured when the device under test is removed. Z open Measure impedance during short circuit Z short , used to obtain the measured impedance Z through equation (4) x The impedance of the device under test is inferred from the middle. （4）； in, To perform bearing complex impedance after open-circuit and short-circuit calibration; The short-circuit impedance measured when the bearing is short-circuited; This refers to the short-circuit complex impedance measured when the bearing is open-circuited; Finally, at the carrier frequency Down, For a single-bearing motor, the parallel capacitance is the equivalent circuit of the bearing impedance, where the power supply carrier frequency is the frequency. C DUT and parallel resistors R DUT The calculation is as follows: （5）； （6）； For a dual-bearing rotary motor, an improved three-arm AC unbalanced Wheatstone bridge is used to measure the impedance of the two bearings. Specifically, based on the original AC unbalanced Wheatstone bridge, a branch with the same structure as the left arm is added next to the right arm, and a reference impedance is set at the top of the arm. The lower part is connected to the second bearing to measure the impedance. The voltage difference between the output terminals of the two bridge arms on the right is denoted as . This is used to reflect the bridge voltage signal of the second bearing branch; by measuring separately and And in combination with the corresponding frequency converter voltage Using the reference impedance parameters, the complex impedances of the two bearings without open-circuit or short-circuit calibration are obtained, and the calculation formulas are as follows: （7）； （8）； in, , , , The complex impedance of the bearing connected to the left side of the bridge when it has not been calibrated with an open-circuit and short-circuit circuit is given. The complex impedance of the bearing connected to the right side of the bridge when it has not been calibrated with an open circuit and short circuit. Finally, the calculated uncalibrated complex impedance is... and As measured impedance respectively Substituting into formula (4) for open-circuit-short-circuit calibration, the calibrated bearing complex impedance is obtained. and ; and then and As respectively Substituting into formulas (5) and (6), the equivalent capacitances of the two bearings are calculated. and equivalent resistance ; Step 7: Send the calculated complex impedance to a remote computer for visualization using computer software.

2. The method for in-situ measurement of complex impedance of motor bearings according to claim 1, characterized in that: The digital differential oscilloscope acquires data at a predetermined sampling rate and sampling interval, and uses the differential voltage probe CH1 to measure the inverter power supply voltage. v gen The differential voltage probe CH2 was used to measure the bridge voltage. v m .

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